A conventional multi-point lock disclosed in U.S. Pat. No. 6,264,252 is for use in a sliding door, and includes two hook members, two rotary operating members, two rod members each of which is pivotally connected between a respective one of the hook members and a respective one of the rotary operating members, and an interlink member that pivotally interconnects the rotary operating members. When one of the rotary operating members is rotated to drive rotation of the corresponding one of the hook members via the corresponding one of the rod members, the other one of the hook members is also driven to synchronously rotate via the interlink member, the other one of the rotary operating members and the other one of the rod members. However, such a structure is relatively complex. Moreover, the hook members may easily be rotated non-synchronously after long term use of the conventional multi-point lock.
Referring to FIGS. 1, 2 and 3, a conventional two-point lock disclosed in U.S. Pat. No. 8,376,414 is for use in a sliding door, and includes an outer casing 1, a locking unit 2 movably mounted to the outer casing 1, and an adjusting unit 3 disposed between the outer casing 1 and locking unit 2 and operable to move the locking unit 2 relative to the outer casing 1. The locking unit 2 includes a mounting casing 201 that is movable relative to the outer casing 1 in a first direction, two hook members 202 that are pivotally mounted to the mounting casing 201, an actuating plate 203 (see FIG. 3) that is movable relative to the mounting casing 201 in a second direction transverse to the first direction for driving rotation of the hook members 202, a rotary operating member 204 that is pivotally mounted to the mounting casing 201, a link member 205 (see FIG. 3) that is pivotally connected between the actuating plate 203 and the rotary operating member 204, and a torsion spring 206 (see FIG. 3) that is disposed between the rotary operating member 204 and a rod portion 207 of the mounting casing 201. Each of the hook members 202 has a driven pin portion 208 (see FIG. 3). The actuating plate 203 has two actuating grooves 209 (see FIG. 3) respectively and slidably engaged with the pin portions 208 of the hook members 203.
When the rotary operating member 204 is rotated to move the actuating plate 203 in the second direction via the link member 205, the hook members 202 are driven by the actuating plate 203 to perform locking or unlocking operation. However, with particular reference to FIGS. 1 and 2, to adjust an extent (H) by which the hook members 202 extend out of the outer casing 1, the adjusting unit 3 is operated to move the whole locking unit 2 relative to the outer casing 1. In other words, the conventional two-point lock of U.S. Pat. No. 8,376,414 employs such a structure that includes inner and outer casings (i.e., the mounting casing 201 and the outer casing 1) in order to adjust the extent (H) by which the hook members 202 extend out of the outer casing 1. Such double-casing structure may increase the weight of the whole conventional two-point lock, and increase the manufacturing cost of the conventional two-point lock as well.
Moreover, with particular reference to FIG. 3, the rotary operating member 204 is simply pivotally connected to the link member 205, and a lengthwise extending line of the rotary operating member 204 cooperates with a horizontal line to form a relatively small angle (θ, about 35 degrees) therebetween when the hook members 202 are at an unlocking position. As such, in the beginning of the operation of the rotary operating member 204 to move each of the hook members 202 away from the unlocking position, a user needs to rotate the rotary operating member 204 to generate a resultant force (F) much greater than a horizontal component (Fx) thereof that is required for moving the actuating plate 203. In this case, F=Fx/sin θ=Fx/sin 35°=1.7Fx. More specifically, the user needs to rotate the rotary operating member 204 to generate 1.7 times the required force to move the actuating plate 203. Such operation is also laborious. In addition, the torsion spring 206 deforms considerably during the operation of the rotary operating member 204, and may therefore occupy a relatively large space in the outer casing 1.